Proposal: std.regex FFI Backend Selection

Status: Draft Created: 2026-01-31 Affects: Standard library, FFI Related: stdlib-philosophy-proposal.md (approved), platform-ffi-proposal.md (approved)

Summary

This proposal selects the FFI backend for std.regex — Ori’s regular expression library.

Problem Statement

The stdlib-philosophy-proposal lists std.regex with “TBD (PCRE2 or RE2)” as the FFI backend. We need to decide:

  1. Which regex engine to use
  2. What syntax/features to support
  3. How to handle WASM

Candidates

PCRE2

Perl-Compatible Regular Expressions, version 2.

Pros:

  • Feature-rich (lookahead, lookbehind, backreferences, Unicode)
  • Widely used and well-documented
  • JIT compilation for performance

Cons:

  • Complex feature set may encourage slow patterns
  • Potential for catastrophic backtracking (ReDoS)
  • Larger binary size

RE2

Google’s regular expression library.

Pros:

  • Guaranteed linear time (no catastrophic backtracking)
  • Good Unicode support
  • Predictable performance

Cons:

  • No backreferences
  • No lookahead/lookbehind
  • May surprise users expecting PCRE features

rust-regex (via C API)

Rust’s regex crate with potential C bindings.

Pros:

  • Memory-safe
  • Good performance
  • Balances features and safety

Cons:

  • Requires building C bindings
  • Rust runtime dependency

Pure Ori

Implement regex engine in Ori.

Pros:

  • Full control
  • Consistent cross-platform behavior

Cons:

  • Massive undertaking
  • Performance unlikely to match C implementations

Feature Comparison

FeaturePCRE2RE2rust-regex
BackreferencesYesNoNo
LookaheadYesNoNo
LookbehindYesNoNo
UnicodeYesYesYes
Named groupsYesYesYes
Linear timeNoYesYes
JITYesNoNo

WASM Considerations

For WASM targets:

  1. JavaScript RegExp: Use browser’s regex via extern "js"
  2. Compile engine to WASM: Use same engine, compiled to WASM
  3. Pure Ori fallback: Limited feature set for WASM

Open Questions

  1. Should Ori guarantee linear-time regex (preventing ReDoS)?
  2. Is the lack of backreferences acceptable?
  3. Should syntax be Perl-compatible or RE2-compatible?
  4. What’s the priority: features vs. safety?

Recommendation

Tentative: RE2

Rationale:

  • Linear time guarantee aligns with Ori’s “if it compiles, it works” philosophy
  • Predictable performance is more important than exotic features
  • Users needing backreferences can use community packages

This is subject to community feedback.

References